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Old 09-20-2013, 09:20 AM   #1
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Grout "weak"


I tiled and grouted my dining room about 6 months ago and am already seeing the grout crack and chip.

The subfloor was 3/4" OSB which i screwed down (it was just nailed and squeaky from the builder), then screwed durock cement board.

I used this grout:
http://www.lowes.com/pd_361282-70680...ductId=3478041

This mortar as the floor does give slightly (weak joists at their max length ):
http://www.lowes.com/pd_361027-70680...ductId=3477941

And this grout sealer (mixes in the with grout):
http://www.lowes.com/pd_304822-70680...ductId=3078695

I hope that grout sealer didn't mess with the strength because it seems a bit... weak. It still comes up when i have to scrub fairly hard to clean up something that gets on it, for instance. Would a surface-applied sealer help prevent further decay or is it too late and I'll have to cut out the offending bits and regrout?

I did my living room with the same materials with the exception of no grout booster and while there are some cracks (the floor moves a LOT), no chipping is occuring and the grout doesn't seem as soft.

EDIT: I didn't see the Tiling subforum.


Last edited by dengle; 09-20-2013 at 11:56 AM. Reason: wrong forum
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Old 09-20-2013, 03:55 PM   #2
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Grout "weak"


Cheer up---I moved this to tile----

If you can scrape the grout out with a knife and it crumbles---you have bad grout---

If it is cracking and chunks come loose ,but the loose chunks are really hard--you may have floor movement issues---

It sounds like you might have both things going on---Did you put mortar under the backer board before nailing?

How long are the floor joists from support to support? how big? How far apart?

A lot of problems surfaced here from folks that used 'Grout Boost" So that might have added to the problems----

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Old 09-20-2013, 04:07 PM   #3
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Grout "weak"


actually, no, I didn't mortar under the backer It was my first floor tile job and unfortunately that point wasn't made clear when I asked the big box people on floor prep. I should have checked here first...

Joists are engineered I's 10 inchers and at 20-22 feet span which is inches from the theoretical max (I looked it up). The part that's really cracking and chipping is right over the main steel I beam though, so can't imagine THAT much movement is occurring unless it's from the whole floor flexing more than that area.

I haven't tried a knife and to be honest, I'm a big hesitant to as well! Then I'll really have to redo the grout!

Let's assume the grout is shoddy, I presume remove the grout and just redo it with straight grout and then top seal it instead? Can the grout be done in sections? It's a "live" area that will be very hard to quarantine fully due to little ones.
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Old 09-20-2013, 09:49 PM   #4
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Grout "weak"


Over the support beam is a good place to crack.

If you have two joists meeting there, then they flex there. You have the "teeter totter effect" going on. When the middle of the floor joist goes down, the end comes up.

If you have one long joist, I wonder if the same thing doesn't happen anyway.

Sure should have had mortar under the tile backer.

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Old 09-20-2013, 10:27 PM   #5
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Grout "weak"


Dengle,

No mortar under the tile backer guarantees you grout cracks eventually. You also have other issues with the span and flexing.

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Old 09-23-2013, 01:16 PM   #6
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Grout "weak"


After re-inspection, it's not the whole floor, it's only two or three grout lines of a few tiles, all near that I-beam (and right in foot traffic/most obvious). I recall that's also where I finished grouting the room.

I'm thinking it's two parts. One, the joists are flexing there the greatest from what you guys think in combination with not mudding the back of the backer board. and two, It's quite possible the grout was starting to set a bit by the time I got there (it was my first job and it took me a while to get in the groove). Luckily my mistake of not grouting under the backer doesn't seem to be affecting the remainder of the room. If I just have to scrape out a few lines of mortar and redo every few years, I'll consider it a painful lesson learned and maybe see if adding some latex additive to help with the flex will help in the future.

Thanks for the input!
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Old 09-23-2013, 05:28 PM   #7
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Grout "weak"


A grout saw is a helpful tool-----------
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Old 09-23-2013, 06:15 PM   #8
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Grout "weak"


At this point that's all you can do. When backer boards are not mortared, you'll likely only have a few small areas that show grout cracks, not the entire floor. You can have hairline cracks and never know it though.

Get a grout saw as Mike suggested, or a multi-tool with the appropriate blade to remove the grout for your repairs.

I'm surprised they carry that "basic" grout and not polymer modified grout like most others. Obviously they want to sell you grout boost, which is another story in itself.

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Old 09-23-2013, 06:20 PM   #9
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Grout "weak"


Or replace grout with epoxy grout may give you a fighting chance.

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